1. Field of the Invention
The present invention relates to a method and a device for evaluating restitution characteristics of a golf club head, such as a hollow metallic golf club head, which are used for evaluating restitution characteristics of an impact surface of the golf club head when the golf club head strikes a golf ball.
2. Description of the Related Art
Golf club manufacturers have proposed a variety of golf clubs having golf club heads with good restitution characteristics so that even low-power golfers are capable of driving a golf ball over a long distance. This has been achieved through improvements in, and development of, golf club head structures and materials.
Furthermore, an assessment of the restitution characteristics of a golf club head is made by evaluating a coefficient of restitution e found by a measurement method proposed by the United States Golf Association (USGA), for example. The USGA requires that the golf clubs used in golf competitions have the coefficient of restitution, e, of 0.830 or less.
The coefficient of restitution e is found by impacting a golf ball perpendicularly with respect to the golf ball impact surface (impact surface) of a golf club head placed on a support stand without a golf club shaft. The coefficient of restitution e is computed from the following equation at the time of impact by using a golf ball's inbound velocity Vin, a golf ball's rebound velocity Vout, a golf club head mass Mn, and a golf ball mass Mb.Vout/Vin=(e·Mh−Mb)/(Mh+Mb)
In contrast, a method capable of easily finding the coefficient of restitution of a impact surface of a golf club head from a first resonance frequency of the impact surface is disclosed in JP 2002-331050 A. Impact vibration is performed on the impact surface without impacting a golf ball onto the golf club head.
Furthermore, a method for estimating the coefficient of restitution of a golf club head by inputting a golf model into a golf club head transfer function and a golf ball impact velocity which are obtained experimentally is disclosed in JP 2003-024477 A. Specifically, the coefficient of restitution e is found from a relationship among the above at the time of impact through the golf ball model.
The coefficient of restitution of the golf club head can be found extremely easily and in a short period of time with the method of JP 2002-331050 A, while the coefficient of restitution can also be suitably found with the method of JP 2003-024477. However, it is still strongly desired to find the coefficient of restitution with high accuracy for a variety of golf club heads having impact surface structures that do not possess uniform thickness.
Furthermore, the method of JP 2003-024477 involves the complexity of preparing a golf ball model in advance when finding the coefficient of restitution e.